1. Field of the Invention
The present invention relates generally to an apparatus and method for determining the time to change automobile engine oil and, more particularly, to an apparatus and method for determining the time to change automobile engine oil, which measure variation in permittivity or electric conductivity of engine oil using a sensor having carbon nanotubes and determine and indicate the time to change the engine oil.
2. Description of the Related Art
Generally, engine oil, which is loaded in an automobile, performs a lubricating function of maintaining the smooth reciprocating motion of a piston, which is performed in response to an explosion in an engine, a sealing function of preventing pressure from leaking, a cleaning function of adsorbing particles in the cylinder and preventing the inner wall of a cylinder from being damaged, and a cooling function of conducting heat away from the cylinder and the piston.
When the engine oil, having the above-described functions, is used for a long time, the amount of injected oil decreases due to combustion by the explosions, and the viscosity, total acid number, and amount of sludge contained in the engine oil vary due to degradation.
Accordingly, the engine oil must be changed periodically. In the case where the time to change engine oil is missed or the operation of an automobile continues without changing the oil, the durability of lubricated parts in an engine requiring lubrication is lowered, the lifespan is reduced, the payment of excessive repair cost are incurred, and the excessive consumption of fuel, attributable to decreased engine output, and environmental problems, attributable to the increase of exhaust gas, also result.
Accordingly, periodical checks must be performed on the engine oil, and the change time must be determined according to the condition of the engine oil. For these purposes, a driver determines the time to change the engine oil based on the driven distance indicated on an integrated meter in a cluster mounted on an instrument panel, or determines the time to change the engine oil by observing a dipstick, which is provided in an engine compartment, with the naked eye, measuring the amount of engine oil, and viscosity and color thereof, and determining the extent of the degradation of the engine oil.
As described above, the conventional method of determining the time to change engine oil is disadvantageous in that it is inconvenient for a driver to personally calculate the driven distance and to personally check the extent of the degradation of the engine oil.
Furthermore, the extent of the degradation of the engine oil is determined through the driver's subjective observation and is thus inaccurate. Accordingly, a disadvantage occurs in that waste and environmental pollution result from unnecessary engine oil changes, and the wear of respective lubricated parts within an engine results from excessively late changes, so that the durability thereof is lowered.
Furthermore, a disadvantage occurs in that the extent of the degradation of the engine oil varies according to the driver's driving habits, so that the actual change time differs from that recommended in a maintenance guide book, therefore it is difficult to determine the change time.
In order to solve the above-described disadvantages incurred by determining the time to change the engine oil by using the naked eye to observe variation in viscosity and color, a technology has been proposed in Korean Pat. Appl. No. 1997-54022, that, when the change times of respective consumable supplies for an automobile are set based on a driving distance and then an accumulated driving distance reaches the set driving distance, alarms at the driver of the time to change the consumable supplies, such as engine oil, brake oil, an air filter, and brake disks.
Furthermore, Korean Pat. Appl. No. 1996-63422 proposed a technology that passes near infrared rays through oil and determines the time to change the oil based on the level of the received rays.
However, in the former case, the time to change the respective consumable supplies provided in an automobile is based on an accumulated driving distance, so that, for the respective consumable supplies, and particularly for engine oil, considerable difference in the extent of the degradation thereof occurs due to variation in drivers' driving habits, unnecessary idling, or other reasons. Accordingly, the former case is disadvantageous in that it is inaccurate, so that the engine oil is not changed at the proper time, therefore economic waste is incurred and the durability of the engine is lowered.
Furthermore, the latter case is disadvantageous in that the time to change the oil cannot be detected if a near infrared ray radiating or receiving element is damaged, normal determination of the change time cannot be performed in the state in which the amount of oil is low, the change time cannot be accurately detected because the degree of transparency of oil is different for each manufacturing company, which thereby decreases the reliability of detection.
Furthermore, since the degradation of engine oil occurs due to variation according to numerous physical and chemical aspects, the method of determining the time to change the engine oil simply by measuring variation in viscosity or color is limited.
Meanwhile, recently, as the fact that the extent of degradation of engine oil is closely related to variation in permittivity and electric conductivity, which are electric characteristics of the engine oil, become known, research into methods of detecting the condition of engine oil by measuring the electrical characteristics of the engine oil is being conducted.
Meanwhile, although a method of using output voltage, Alternating Current (AC) impedance, and viscosity is employed by foreign companies, the commercialization of resulting products has been delayed because the method seems to have some problems.
Meanwhile, measuring variation in electric conductivity or permittivity, which is caused by various physical and chemical variations in engine oil, is advantageous in that it allows information about variation in engine oil to be easily acquired.
However, until now, measuring apparatuses using electric conductivity or permittivity have a cylinder or parallel plate form that is voluminous, therefore are disadvantageous because they are not compact and mass-produced.